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A neutron diffraction study of four rare-earth phosphate glasses of composition (R2O3)x(P2O5)1-x, where x = 0.197, 0.235, 0.187, 0.263 and R = Ce, Ce, Nd, Tb respectively is presented. The structures of these materials were investigated as a function of (a) rare-earth atomic number and (b) composition. The results show that samples containing the larger rare-earth ions (Ce3+ and Nd3+) are coordinated to seven oxygen atoms whereas the immediate environment of Tb3+ ions is six coordinate. This implies that rare-earth clustering must be present in the samples containing larger rare-earth ions although no R ... R correlations are directly observed. Terminal and bridging P-O correlations are resolved, existing in an approximately 1:1 ratio. Second-neighbour O(P)O separations are located with good accuracy and P(O)P correlations relating to the bridging chain are observed. There is also first evidence for the third neighbour correlation, P(OP)O, at ~2.8 Å. A residual feature in the neutron diffraction data, present at ~1.8 Å, is interpreted as Al-O correlations on the basis of 27Al MQMAS NMR experiments. This aluminium impurity originates from the use of aluminium oxide crucibles used in the glass synthesis and is shown to exist as a mixture of octahedral, tetrahedral and penta-coordinated Al-O species. No structural perturbations of the overall network were observed with varying sample composition.

A variable-temperature (79, 145, and 293 K) extended x-ray absorption fine structure study, using rare-earth L III absorption edges, is reported for phosphate glasses doped with rare-earth elements (R, where R ‫ס‬ La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, and Er) with compositions close to metaphosphate, R(PO 3 ) 3 . The results yield nearest-neighbor R-O distances that demonstrate the lanthanide contraction in a glassy matrix and an R-O coordination intermediate between 6 and 7 for rare-earth ions with smaller atomic number (Z) and 6 for rare-earth ions with larger Z. Thermal parameters show no significant changes in R-O distances or coordination numbers between 293 and 79 K. There is evidence of an R-P correlation between 3.3 and 3.6 Å and the beginning of a second R-O correlation at approximately 4 Å. No R-R correlations up to a distance of approximately 4 Å were observed.

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The version in the Kent Academic Repository may differ from the final published version. Users are advised to check http://kar.kent.ac.uk for the status of the paper. Users should always cite the published version of record.